#generates a matrix of std dev values in classes
#        attr1   attr2   attr3   attr4 ...
#class1
#class2
#class3
#class4
function S = getStdevs(data)
    S=[];
    for i=1:4
        subset=data(data(:,1)==i,2:end);
        S=[S;sqrt(var(subset))];
    end;
end

